I'm using Gentoo with OSS 4, with an Intel HDA device. Playback works flawlessly, but recording is something I can't get working. My current physical setup is very simple: stereo output on the green jack, and stereo input on the pink jack.

I have noticed that, oddly, by default, jack.pink.mode = front. From what I can gather, it really should be input, so I have tried changing it to that.

Doing this has the interesting effect of any input to the pink jack being echoed back to the green jack, or in other words, I can hear what I am saying. I have also noticed that setting misc.input-mix-mute1 = OFF disables this echoing.

However, nothing I have tried makes the input show up in the vmix0-invu or even reach vmix0, nor can I record with Skype (the 2.0.0.72 version, statically linked for OSS) or ossrecord.

The reason you the echo is because jack.pink sets (I believe) passthrough volume, definitely not record volume. Recording volume is set by misc.mic or record.mix (don't exactly recall). You can then test recording via 'ossrecord - | ossplay -".